Weather Forecast

Hawaii County Weather Forecast for March 21, 2021

March 21, 2021, 7:16 AM HST
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Hilo

Today: Occasional showers. High near 75. West northwest wind 5 to 9 mph becoming east northeast in the morning. Chance of precipitation is 100%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Occasional showers. Low around 63. Northeast wind 5 to 7 mph becoming calm. Chance of precipitation is 80%. New precipitation amounts of less than a tenth of an inch possible.

Monday: Occasional showers, with thunderstorms also possible after noon. High near 76. West southwest wind around 5 mph becoming light and variable in the morning. Chance of precipitation is 80%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Kona

Today: Scattered showers and thunderstorms after 1pm. Partly sunny, with a high near 80. Calm wind becoming west northwest 5 to 7 mph in the afternoon. Chance of precipitation is 50%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers and thunderstorms. Mostly cloudy, with a low around 61. Light and variable wind. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

ARTICLE CONTINUES BELOW AD

Monday: Scattered showers before 7am, then scattered showers and thunderstorms after 1pm. Mostly sunny, with a high near 79. Calm wind becoming west 5 to 7 mph in the afternoon. Chance of precipitation is 50%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Waimea

ARTICLE CONTINUES BELOW AD

Today: Occasional showers. High near 75. Windy, with a northeast wind around 23 mph, with gusts as high as 33 mph. Chance of precipitation is 80%. New precipitation amounts between three quarters and one inch possible.

Tonight: Occasional showers, mainly before 7pm. Low around 52. Breezy, with a northeast wind 14 to 22 mph, with gusts as high as 32 mph. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.

Monday: Scattered showers, then occasional showers and possibly a thunderstorm after 1pm. High near 74. North northeast wind 7 to 13 mph. Chance of precipitation is 80%. New rainfall amounts between a quarter and half of an inch possible.

Kohala

ARTICLE CONTINUES BELOW AD

Today: Occasional showers. High near 71. Very windy, with an east wind 26 to 31 mph, with gusts as high as 50 mph. Chance of precipitation is 100%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Occasional showers. Low around 45. Windy, with an east wind 22 to 26 mph, with gusts as high as 38 mph. Chance of precipitation is 90%. New precipitation amounts of less than a tenth of an inch possible.

Monday: Occasional showers, with thunderstorms also possible after noon. High near 70. Breezy, with an east wind 17 to 22 mph decreasing to 5 to 10 mph in the morning. Winds could gust as high as 31 mph. Chance of precipitation is 90%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

South Big Island

Today: Scattered showers, mainly after noon. Mostly sunny, with a high near 80. Very windy, with an east northeast wind 26 to 31 mph, with gusts as high as 40 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Isolated showers. Partly cloudy, with a low around 69. Windy, with an east northeast wind 20 to 26 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Monday: Scattered showers and thunderstorms after noon. Mostly sunny, with a high near 79. Windy, with an east northeast wind 15 to 24 mph, with gusts as high as 30 mph. Chance of precipitation is 30%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Puna

Today: Occasional showers. High near 74. Northwest wind 7 to 14 mph becoming northeast in the morning. Winds could gust as high as 20 mph. Chance of precipitation is 100%. New precipitation amounts between a half and three quarters of an inch possible.

Tonight: Occasional showers. Low around 61. North northeast wind 7 to 11 mph becoming west northwest after midnight. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.

Monday: Occasional showers, with thunderstorms also possible after noon. High near 75. West northwest wind 5 to 8 mph becoming east in the afternoon. Chance of precipitation is 80%. New rainfall amounts between a quarter and half of an inch possible.

Waikoloa

Today: Isolated showers after noon. Mostly sunny, with a high near 81. Very windy, with an east northeast wind 15 to 20 mph increasing to 26 to 31 mph in the morning. Winds could gust as high as 50 mph. Chance of precipitation is 20%.

Tonight: Isolated showers. Partly cloudy, with a low around 61. Windy, with an east wind 20 to 25 mph decreasing to 8 to 13 mph after midnight. Winds could gust as high as 36 mph. Chance of precipitation is 20%.

Monday: A 20 percent chance of showers and thunderstorms after noon. Mostly sunny, with a high near 80. West northwest wind 6 to 11 mph becoming light and variable in the afternoon.

Detailed Forecast

Synopsis

Wet trade wind weather will prevail this morning before giving way to a drier pattern this afternoon and tonight, particularly across the smaller islands. Breezy to windy trades will persist today, with the trades beginning to slowly ease tonight. Drier trade wind weather will continue on Monday, with winds lowering further. As a front moves closer Monday night and Tuesday, a land and sea breeze pattern will develop, with showers favoring areas near the coast Monday night and the island interiors on Tuesday. More unsettled weather may develop Tuesday night and linger through late next week as a front moves into the island chain and stalls out.

Discussion

Currently at the surface, a 1038 mb high is centered around 1500 miles northeast of Honolulu, while a cold front is located around 1200 miles west-northwest of Kauai. The strong high is driving breezy to windy trades across the island chain early this morning. Infrared satellite imagery shows mostly cloudy skies in windward areas, with partly cloudy conditions in most leeward locales. Radar imagery shows numerous showers moving into windward areas of most islands, with showers spreading leeward fairly regularly due to the strength of the trades. Main short term concerns revolve around Wind Advisory headlines today and trade wind trends during the next couple days.
Strong high pressure northeast of the islands will keep breezy to windy trades in place across the island chain today. The trades will likely continue to reach advisory thresholds in some of the windier areas of Maui County and the Big Island, and as a result, the Wind Advisory has been extended through 6 PM this evening for these areas. The trades will then trend down tonight, lower to moderate levels on Monday, then become light and variable Monday night and Tuesday with land breezes and sea breezes developing in many areas. As an approaching front moves closer to the islands Tuesday night and Wednesday, south to southwest flow is expected to increase to moderate levels across the state. The front appears to shift into the central islands Wednesday night and Thursday, then stall out and weaken as it shifts slowly westward Thursday night and Friday. Moderate north to northeast winds will likely develop behind the front over the western islands, with moderate south to southeast winds holding in place over the eastern end of the state. As the front weakens late next week, winds should shift back to a more typical trade wind direction late Friday, with moderate trades then building back over the entire island chain next weekend as high pressure builds to the north of the state.
As for the remaining weather details, a wet trade wind pattern appears to hold in place this morning, with conditions beginning to dry out this afternoon over Oahu and Kauai, and over Maui County tonight. Shower coverage will remain a bit higher over windward Big Island through Monday however, but we should see a gradual drying trend here as well. Fairly dry weather should hold in place across much of the state Monday night and Tuesday, with showers favoring locations near the coast at night and over the island interiors during the afternoon in the light wind regime. In addition, the airmass appears unstable enough that a thunderstorm could pop over the Big Island slopes each afternoon through Tuesday. More unsettled weather appears in store Tuesday night through late next week as southerly flow lifts some deep tropical moisture northward into the islands while a front moves into the area and stalls out. There is still quite a bit of uncertainty on how much rain can be expected and where the front may end up stalling out, so will follow a blended forecast approach until details become more clear.

Aviation

Strong easterly trade winds will hold through tonight, then begin to ease through the day Monday as high pressure passes to the north. A band of moisture that has drifted south into the area combined with an upper trough will keep the rain chances in the forecast today, especially through the morning hours. Although most of the rainfall will continue to focus over the typical windward and mountain locations, some will carry over into leeward sections of the smaller islands. For the leeward sections of the Big Island, a few showers could become heavy and a thunderstorm or two can’t be ruled out this afternoon. MVFR CIGS/VSBYS are expected in and around passing showers.
AIRMET Sierra remains in effect for mountain obscurations over the north and east slopes of Kauai, Oahu, Molokai, Maui, and the Big Island.
AIRMET Tango remains in effect for low-level moderate turbulence over and south through west of all island mountains due to strong trade winds. This AIRMET will remain in effect at least through Sunday. AIRMET Tango for strong surface winds greater than 30 knots also remains in effect.

Marine

High pressure positioned north to northeast of the state will continue to produce fresh to strong trade winds across the Hawaiian waters through tonight. While the most recent satellite passes have not observed gale force winds within the Alenuihaha Channel, areas 30 knot sustained winds do suggest probable frequent gusts to gale in the channel. Therefore, the Gale Warning will continue for the Alenuihaha Channel through this afternoon. Fresh to strong trade winds, along with a north northeast swell, will maintain rough seas into the evening hours. The Small Craft Advisory has been extended through 6 AM HST Monday for the remaining coastal waters due to winds and/or seas. Winds will weaken and veer more southerly with resultant lowering seas Monday as a cold front approaches the area from the northwest. The front is forecast to reach the northwest coastal waters by Wednesday then stall across the central waters Thursday.
The short period east trade wind swell will peak today into tomorrow and then gradually lower through the week. This will be in direct response to weakening trades that will transition to light southerlies through mid week with the approach of a front northwest of the state. A High Surf Advisory (HSA) remains in effect for the exposed eastern shores of Kauai, Oahu, Molokai, Maui and Big Island through 6 AM HST Monday. An extension to this HSA may be needed through Monday afternoon. The small north northeast swell that filled in this weekend will linger through Tuesday. A couple of small, short period northwest swells will move through the islands through Tuesday. A small compact low approximately 800 nm south of the Aleutian Islands this morning will send the next appreciable northwest swell our way. This northwest swell is scheduled to arrive Tuesday night and travel down the chain through Thursday. Surf heights along north and west facing shores may reach low end HSA criteria Thursday during the swell’s peak. This northwest swell will gradually subside Friday and Saturday. A series of storms south of New Zealand are sending pulses of long period swell energy toward the local waters. These very small, long period south swells could arrive as early as Tuesday night and provide a small boost to mid to late week south shore surf.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Monday for Kauai Windward, Oahu Koolau, Olomana, Molokai Windward, Maui Windward West, Windward Haleakala, Big Island North and East.
Wind Advisory until 6 PM HST this evening for Molokai, Lanai, Kahoolawe, Maui Windward West, Maui Leeward West, Maui Central Valley, Windward Haleakala, Leeward Haleakala, South Big Island, Big Island North and East, Kohala.
Small Craft Advisory until 6 AM HST Monday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.
Gale Warning until 6 PM HST this evening for Alenuihaha Channel.

Data Courtesy of NOAA.gov

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